1. Field of the Invention
The present invention relates to a discharge energy recovery device and an image forming apparatus employing the discharge energy recovery device.
2. Description of the Background Art
Some image forming apparatuses print images on recording media by jetting ink droplets, in which a piezoelectric element (hereinafter, also referred to as an actuator) is driven when supplied with a given voltage and a large number of piezoelectric elements are driven to form an image. As shown in FIG. 1, current amplification of actuator drive voltage waveform is typically conducted using a bipolar transistor. FIG. 1 shows a typical circuit diagram of a piezoelectric element drive circuit.
In the configuration shown in FIG. 1, base terminals of bipolar transistors Q83 and Q84 constituting a current amplification unit 82 become low (“L”) and an analog switch (SW) 86 is switched ON by a control signal from a recording head controller 81, at which time a voltage +VDD is applied to an actuator 85 actuator charging current A flows to the actuator 85, and a voltage Vcom which is a charged voltage of the actuator 85 flows to ground (GND) as actuator discharge current B.
However, in the conventional current amplification circuit using a bipolar transistor shown in FIG. 1, most of the power to drive the actuator is lost as heat from the bipolar transistor, resulting is wasted power consumption. Although many patent applications disclose configurations to recover the actuator discharge current B of actuator to reuse as the power to drive the actuator (actuator drive power), none of these considers the effect on the actuator drive voltage waveform itself (e.g., irregular waveform, hindering actuator drive control).
JP-2002-103603-A discloses a configuration to reduce power consumption by effectively using electric energy accumulated in one or more actuators, in which actuator discharge current is charged to two charging capacitors, and then the power charged to the charging capacitors is reused as power to drive the actuators.
However, because large-capacity capacitors are used as the charging capacitors the charging time of the capacitors lengthens, thereby slowing the drive cycle of the actuators themselves. Further, a charging current to the actuators and a discharge current from the actuators vary depending on the number and capacitance of the actuators actually driven. Due to such fluctuation, the charge amount to be charged to one or more charging capacitors also fluctuates. As a result, the rising time and falling time of drive voltage pattern or waveform of the actuators fluctuate, hindering control of the drive voltage pattern.